It has been conventional to operate an object (hereinafter, referred to as a “target object”) which is displayed on a two-dimensional screen of a display device to three-dimensionally move the target object using an input device such as a mouse or the like. An operation of three-dimensionally moving the target object is applied when an observed object (hereinafter, referred to as a “reference object”) is observed from various positions, for example, by using a virtual camera as a target object. That is, the reference object is allowed to be viewed from various positions by moving three-dimensionally the virtual camera around or within the reference object and by changing the view point position.
When a target object is to be operated to move three-dimensionally by a two-dimensional input device such as a mouse or the like, it is known to operate the target object to move by using two screens of an x-y plane and an x-z plane, for example. In the above operation, the target object is displayed respectively on the x-y plane and the x-z plane, and the target object is operated to move two-dimensionally first on the x-y plane and to move two-dimensionally then on the x-z plane thereby to realize a three-dimensional moving operation.
The method described above is suited to accurately operate a target object. However, since the target object is operated on two screens, the operation amount may be greatly increased and the time taken for the operation may increase in particular when a target object is to be operated so as to move complicatedly.
On the other hand, it is known to generate a local coordinate system around a reference object and to determine a path for movement of a target object so as to move the target object along the path according to the moving amount of a mouse. It is allowed to operate the target object to move three-dimensionally with a relatively small operation amount by this method.
However, the degree of freedom of three-dimensional movement of a target object may be restricted sometimes in related art.
That is, since the related art operates the target object to move simply along a path for movement that has been set and fixed in advance, it may be difficult for the related art to move the target object to a position deviating from the path. Therefore, it may be difficult for the related art to observe the reference object from various positions by three-dimensionally moving the target object to an arbitrary position around or within the reference object on a two-dimensional screen.
A technique disclosed herein has been made in view of the above mentioned circumstances and aims to provide an object operation device, an object operation method, and a computer-readable storage medium for storing an object operation program that allow the degree of freedom of three-dimensional movement of a target object to increase by a simple operation.    [Patent Document 1] Japanese Laid-open Patent Publication No. 10-232943